Integrated ion separation spectrometer

ABSTRACT

An apparatus including an ion injector having an inlet and an outlet and a micro-corona ionizer positioned between the inlet and the outlet of the ion injector. The micro-corona ionizer includes a planar electrode and a sharp knife-edged electrode spaced apart from the planar electrode and positioned with the sharp knife edge pointing toward the planar electrode. A drift and separation channel having a first end and a second end is positioned with the first end coupled to outlet of the ion injector, and an ion detector is coupled to the second end of the ion separation and drift channel. Other embodiments are disclosed and claimed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority under 35U.S.C. §120 to, U.S. patent application Ser. No. 12/828,503, filed 1Jul. 2010 and still pending. The priority application in turn claimspriority under 35 U.S.C. §119(e) to U.S. Provisional Application No.61/222,807, filed 2 Jul. 2009.

TECHNICAL FIELD

The disclosed embodiments relate generally to gas detectors and inparticular, but not exclusively, to detectors with integratedcharged-ion separation.

BACKGROUND

Gas detection instruments are used to separate chemical ions from a gasand detect the ions. Existing instruments, however, all have drawbacksthat make them expensive to build, burdensome to operate, and difficultor impossible to miniaturize. An Ion Mobility Spectrometer (IMS) is agas detection instrument in which gas ions are separated according totheir individual velocities as they drift through an electric field.Most traditional large non-portable IMS systems use electro-sprayionization to ionize chemical molecules, but this ionization source istoo complex to be cost-effectively down-sized and integrated with othercomponents. Other ionization techniques such as surface ionization havebeen used, but most of the ionization techniques require a high-vacuumenvironment for input sample gas, which is very challenging to beimplemented in a miniature IMS system. As a result, a new ionizationsource that can be operated in atmospheric pressure with scalable sizeis necessary.

A small-scale IMS device has been reported by Sandia National Lab, butthis miniature IMS drifter involves too many parts and electricalconnections, which results in much lower device fabrication throughputand much higher package and assembly cost. Moreover, this IMS has ameasured dimension in the range of 10 cm×2 cm×2 cm, but still needsfurther size reduction before it can be used as a fully-assembledhandheld gas detection system.

Draper Labs developed a miniaturized Radio Frequency-IMS (rf-IMS). Thisrf-IMS has significant drift channel size reduction due to thesimplification of the drift or separation electrodes by using High-FieldAsymmetric Waveform Ion Mobility Spectrometry (FAIMS) technology tofilter ions in the drift channel. Such FAIMS technology requires a veryhigh radio frequency (RF) electric field to filter the ions in the driftchannel, with a voltage of 1700V at 2 MHz frequency. The correspondinghigh-voltage RF power supply consumes very high power and also requiresspecial microwave protection. Meanwhile, the electronics for producingsuch high voltage RF signal are very expensive and usually very large,which in turns leads to difficulty in producing a low-cost miniature gasdetector system.

In both current state of the art miniature gas detection systems,radioactive materials were used as the ionization source in order tokeep small system footprint: the Sandia IMS uses radioactive 241Am asits ionization source to reduce the system size, while the Draper Labsrf-IMS uses radioactive 63Ni as the ionization source. The use ofradioactive materials raises its own problems. Regular leak tests mustbe performed to work with such materials. Meanwhile, special safetyregulations and licensing requirements can limit the commercialacceptance of devices using radioactive material. Radioactive wastedisposal also raises serious concerns about environmental impacts.Therefore, the development of an ambient pressure ionization source thatcan replace radioactive material is desired.

Current miniature gas detectors are still constructed by separateindividual components—separate ionization sources, separate ion driftand separation channels, and separate ion detector—which requiresignificant amount of assembly efforts and thus higher cost. Theseseparate components cannot be monolithically integrated in fabricationand require significant efforts on the assembly, which increases thedevice cost. A more robust miniaturized gas detector that can beinherently integrated for low-cost mass production is desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified. Figures are not drawn to scale unlessspecifically indicated.

FIG. 1A is a high-level block diagram of an embodiment of an ionseparation spectrometer.

FIG. 1B shows a pair of graphs illustrating results that are possiblewith the ion separation spectrometer shown in FIG. 1A.

FIG. 2A is a side view of an embodiment of an ion separationspectrometer.

FIG. 2B is a side view of the embodiment of the ion separationspectrometer shown in FIG. 2A, illustrating an embodiment of electricalconnections that can be used with the spectrometer.

FIG. 2C is a diagram illustrating an embodiment of the operation of theion separation spectrometer shown in FIG. 2B.

FIGS. 3A-3D are diagrams illustrating an embodiment of the constructionof the ion separation spectrometer shown in FIG. 1A.

FIGS. 4A-4B are a side view and a plan view, respectively, of analternative embodiment of an ion separation spectrometer.

FIG. 4C is a side view of an alternative embodiment of the ionseparation spectrometer shown in FIGS. 4A-4B.

FIG. 5A is a plan view of an alternative embodiment of an ion separationspectrometer.

FIG. 5B shows a pair of graphs illustrating results that are possiblewith the ion separation spectrometer shown in FIG. 5A.

FIG. 6 is a plan view of another alternative embodiment of an ionseparation spectrometer.

FIG. 7 is a schematic drawing of an embodiment of a gas analysis systemusing an embodiment of an ion separation spectrometer.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Embodiments of an apparatus, method and system for an integrated ionseparation spectrometer are described herein. In the followingdescription, numerous specific details are described to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention can bepracticed without one or more of the specific details, or with othermethods, components, materials, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail but are nonetheless encompassed within the scope of theinvention.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in thisspecification do not necessarily all refer to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments.

FIG. 1A illustrates schematically an embodiment of an ion separationspectrometer (ISS). The ISS includes three main components: a ionizationand injection section with an inlet and an outlet, an ion drift andseparation channel that has one end coupled to the outlet of theionization and injection section, and an ion detection section coupledto the ion drift and separation channel at the opposite end from wherethe ionization and injection section is coupled to the channel. Allthree elements are aligned substantially along an axis or centerline.

FIGS. 1A and 1B together illustrate the operation of the ISS of FIG. 1A.A gas sample is directed into the ionization and injection section,where chemical atoms or molecules in the gas are ionized and, afterionization, the resulting ion clusters are injected into the drift andseparation channel. In the drift and separation channel, the ions aresubjected to an electric field. Different ions in the ion clusters willhave different charges, different masses, and different cross-sectionalshapes and areas. The force exerted on each ion by the electric fieldwill depend on the ion's charge, and the acceleration of each ion inresponse to the force will depend on it mass. Consequently, subjectingthe ion clusters to an electric field has the effect of separatingindividual ions from the ion clusters and accelerating them at differentrates toward the ion detector, such that different ions will reach thedetector at different times (i.e., they are separated in the timedomain). Since the ions are separated and arrive at the detector atdifferent times, the presence and concentration of the different ionscan be sensed based on the time signature of the signal from the iondetector, as shown in FIG. 1B.

FIG. 2A illustrates an embodiment of an ion separation spectrometer(ISS) 200. The illustrated embodiment is a small-scale micro-ISS thatintegrates the elements of the ISS into a single chip but, with respectto this or any other embodiment disclosed herein, use of the prefix“micro” does not limit the size of the device or any component thereof,as other larger-scale embodiments of the device and/or its componentsare also possible.

ISS 200 includes a first subassembly 202 having some elements of themicro-ISS formed on it, a second subassembly 204 having other elementsof the micro-ISS formed on it and a spacer 206 between them to keep thesub-assemblies at the desired separation when bonded together as shown.The micro-corona-ISS chip can be fabricated, for example, bymicro-electromechanical-systems (MEMS) process on a PCB board or siliconwafer for low-cost mass production. Details of subassemblies 202 and 204are described below in connection with FIGS. 3A-3D. ISS 200 is intendedto be operated in ambient pressure but can also be applicable in vacuumenvironment.

ISS 200 includes four main components: a micro-corona ionizer thationizes chemical atoms and/or molecules in a gas sample entering theinlet; an ion injector to inject the resulting ions into the drift andseparation channel; an ion drift and separation channel; and an ioncollector electrode or detector array. The micro-corona ionizer includesa sharp electrode or probe 214 formed on substrate 208 and a planarelectrode 234 formed on substrate 231. Probe 214 is electrically coupledto a contact pad 216 on the opposite side of substrate 208 by aconductive path 220. Contact pad 216 and conductive path 220 are used toprovide electrical power to probe 214. Similarly, planar electrode 234is electrically coupled to contact pad 236 on the opposite side ofsubstrate 231 by a conductive path 238. Contact pad 236 and conductivepath 238 are used to provide electrical power to planar electrode 234.The sharp probe 214 and the surface of planar electrode 234 are spacedapart by a discharge distance d, which can vary depending, for example,on the voltages to be applied and the chemicals to be ionized in the gassample. The micro-corona ionizer in the ISS chip is thus used to ionizeinput gases/VOCs instead of using radioactive material as an ionizationsource.

The ion injector includes two pairs of injector electrodes. The firstpair of injector electrodes is positioned near the inlet of the ioninjector and includes electrode 210 formed on substrate 208 andelectrode 233 formed on substrate 231. Electrode 210 is separated fromelectrode 233 by distance h1. Electrode 210 is electrically coupled to aconductive path 222 in or on substrate 208, while electrode 233 iselectrically coupled to a conductive path 240 in or on substrate 231.The second pair of injector electrodes is positioned near the outlet ofthe ion injector and includes electrode 212 formed on substrate 208 andelectrode 232 formed on substrate 231. Electrode 212 is separated fromelectrode 232 by distance h2. Electrode 212 is electrically coupled to aconductive path 222 in or on substrate 208, while electrode 232 iselectrically coupled to a conductive path 240 in or on substrate 231.Conductive paths 222 can be used to provide electrical power toelectrodes 210 and 212, while conductive paths 240 can be used toprovide electrical power to electrodes 231 and 232.

In the illustrated embodiment, the two pairs of injector electrodes arelongitudinally spaced apart from each other by distance L1 and themicro-corona ionizer is positioned between the injector electrode pairs.Distance L1 between the pairs of electrodes, as well as the transversedistances h1 and h2 between electrodes, can be determined based on theoperational requirements of ISS 200, such as the voltages to be appliedand the chemicals to be ionized and injected. In the illustratedembodiment the injector electrodes are all of substantially the samesize, but in other embodiments the injector electrodes need not be ofthe same size: the different injector electrode pairs can have differentsized electrodes, the electrodes within each pair can be of differentsizes, or both. Moreover, in the illustrated embodiment the injectorelectrodes are positioned such that the outlet of the ion injector issubstantially aligned with a centerline of ISS 200, but in otherembodiments the injector electrodes can be sized so that the outlet ofthe ion injector is off the centerline of ISS 200.

The ion drift and separation channel is coupled to the outlet of the ioninjector and includes two sets of separation electrodes: a set ofelectrodes 224 formed on the side of substrate 208 that defines a wallof the channel, and a set of electrodes 242 formed on the side ofsubstrate 231 that forms another wall of the channel. Separationelectrodes 224 and 242 are used to create an electric field in the driftand separation channel to separate ions and accelerate them toward thedetector.

Separation electrode sets 224 and 242 are spaced apart from each otherby transverse distance D, and the individual electrodes in each set ofelectrodes are regularly spaced along the substrate in a longitudinaldirection. Distance D, as well as the longitudinal spacing betweenindividual electrodes in each set, can be determined based on theoperational requirements of ISS 200, such as the ions to be separated,voltages to be applied, length L2 of the channel, and so forth. In theillustrated embodiment, the separation electrode sets 224 and 242 eachinclude eight regularly-spaced electrodes, but in other embodiments eachset of electrodes can include any number of electrodes, including asingle (i.e., one) electrode, and the longitudinal spacing betweenindividual electrodes in each set need not be regular. Moreover, in theillustrated embodiment both sets of electrodes 224 and 242 have the samenumber of individual electrodes, but in other embodiments sets ofelectrodes 224 and 242 need not have the same number of individualelectrodes. In still other embodiments, the number of separationelectrode sets can be greater or less than the number shown in theillustrated embodiments. Various types of separation electrodeconfigurations and electric field applications can be used in the driftand separation channel to achieve desired ion separation during theirtravel before reaching the ion detector, as shown in other embodimentsdescribed herein.

Individual electrodes within electrode set 224 are electrically coupledby conductive paths 228 to resistors 226 on the opposite side ofsubstrate 208 and, similarly, individual electrodes within electrode set242 are electrically coupled by conductive paths 246 to resistors 244 onthe opposite side of substrate 208. Among other things, resistors 226and 244 can be used to heat the drift and separation channel. Conductivepaths 228 and 246 also provide an electrical coupling between theelectrodes and resistors and electrical source so that electrical powercan be supplied to the electrodes and resistors. In the illustratedembodiment, the number of individual resistors matches the number ofelectrodes, but in other embodiments that need not be the case.

The ion detector is positioned at the end of the drift and separationchannel opposite the end where the channel is coupled to the ioninjector. The ion detector has a longitudinal dimension L3,corresponding roughly to the distance between the last individualseparation electrode and the sensor or detector. In the illustratedembodiment, the sensor includes sensor electrode (also referred to as a“sense electrode”) 230 formed on substrate 208 and a sensor electrode248 formed on substrate 231. Sensor electrode 230 is electricallycoupled to a conductive path 229 that leads to the side of substrate 208opposite the side where electrode 230 is formed, while sensor 248 iselectrically coupled to a conductive path 249 that leads to the side ofsubstrate 231 opposite the side where electrode 248 is formed.Conductive paths 229 and 249 provide a way for circuits and associatedlogic to be coupled to electrodes 230 and 248 to read, condition andprocess signals generated by electrically charged ions received at thesensor electrodes. The presence and/or concentration of specific gasesor chemicals can be determined based on the spectrum signature of thesignals from the sensor electrodes. In the illustrated embodiment twosensor electrodes of similar size are shown at the same longitudinalposition, but other embodiments can include a lesser or greater numberof electrodes and in other embodiments the electrodes need not be at thesame longitudinal position and need not have the same size.

FIG. 2B illustrates an embodiment of the electrical connections that canbe used for ISS 200. A switched direct-current (DC) high voltage (DC-HV)source 252 is electrically connected to probe 214 through contact pad216 and conductive path 220, and is also electrically connected toplanar electrode 234 through contact pad 236 and conductive path 238.Switched DC-HV source 252 can apply high voltages between probe 214 andplanar electrode 234 to ionize chemicals in a gas sample injected intoISS 200. The exact voltage applied by DC-HV source 252 can depend onfactors such as the separation distance d and the chemicals to beionized, while the duration of the switched high voltage can vary fromnanoseconds to greater than milliseconds depending on the operationalrequirements. In one embodiment, DC-HV source 252 can apply voltagesbetween 0V and 1000V, but in other embodiments it can apply voltagesoutside this range.

The injector electrodes are similarly connected to separate DC highvoltage (DC-HV1) sources. Injector electrodes 210 and 212 are coupled toDC-HV1 source 254 through conductive paths 222, while injectorelectrodes 231 and 232 are coupled to DC-HV1 source 256 throughconductive paths 240. The voltages applied by DC-HV1 source 254 andDC-HV1 source 256 will determine the initial ion injection velocity intothe drift and separation channel. In one embodiment, DC-HV1 sources 254and 256 can apply voltages between 0V and 1000V, but in otherembodiments they can apply voltages outside this range.

Electrode sets 224 and 242 are electrically coupled to the same orseparate DC high-voltage (DC-HV2) sources. Electrode set 224 is coupledto DC-HV2 source 258 through conductive paths 228, while electrode set242 is coupled to DC-HV2 source 260 through conductive paths 246. Withelectrode sets 224 and 242 uniformly spaced apart by distance D, andindividual electrodes regularly spaced within each set, the voltagesapplied by DC-HV2 source 258 and 260 produce a uniform longitudinalelectric field along the ion travel direction. The HV2 voltage willdetermine the ion drift time before reaching the detector. In oneembodiment, DC-HV2 sources 258 and 260 can apply voltages between 500Vand 1000V, but in other embodiments they can apply voltages outside thisrange.

Detector electrodes 230 and 248 are electrically coupled to circuitryand logic 262 to read, condition and/or process signals received fromthe detector electrodes for quantitative gas ion analysis. Detectorelectrode 230 is coupled to circuitry and logic 262 through conductivepaths 229, while detector electrode 248 is coupled to circuitry andlogic 262 through conductive paths 249.

FIG. 2C diagrammatically illustrates the operation of an embodiment ofISS 200 having the electrical connections shown in FIG. 2B. When gasanalytes are introduced to ISS 200, for example by a gas chromatographas shown in FIG. 7, the micro-corona ionizer is pulse-switched, whichionizes the input gases/chemicals. If not already resolved (separated)by another component such as a gas chromatograph, the micro-coronaionizer simultaneously creates ion clusters from differentgases/chemicals. The ion clusters are then swept into the ion drift andseparation channel by the ion injector (if an injection voltage isapplied, DC-HV1≠0) or by gas flow (if no injection voltage is applied,DC-HV1=0). Different ions have different mass and correspondingcross-section resistance when traveling through the ambient within thedrift and separation channel. The ion clusters are then separated intime and sensed by the ion detector/electrode due to different travelingvelocities along the drift and separation channel. By evaluating the ioncurrent signal pattern received from the sensor electrodes, specificgases/chemicals that are not separated by other devices such as a gaschromatograph can be further distinguished by ISS 200. The ion signalstrength determines the corresponding input chemical concentration.

FIGS. 3A-3D illustrate an embodiment of the construction of firstsubassembly 202 and second subassembly 204, which are bonded togetherwith spacer 206 to form ISS 200 (see FIG. 2A). FIGS. 3A-3B togetherillustrate an embodiment of the construction of first subassembly 202.Subassembly 202 includes a substrate 208 having several componentsformed thereon. Probe 214, injector electrodes 210 and 212, electrodeset 224 and detector electrode 236 are formed on one side of substrate208, while resistor set 226 and contact pad 216 are formed on the otherside of substrate 208. In one embodiment all the electrodes can be metaland can be fabricated to desired sizes by electroplating or directprinting, but in other embodiments semiconductors or other non-metalconductors can be used for electrodes. In other embodiments, differentfabrication approaches are also possible. For example, where ISS 200,and hence subassembly 202, is to be a small-scale device, such as aMEMS-scale device, processes such as photolithographic patterning andetching can be used (see, e.g., FIGS. 4A-4C).

Substrate 208 can be any kind of substrate that can support thecomponents formed on it and that can withstand the manufacturing andoperating conditions that will be faced. In one embodiment, substrate208 can be a single-layer or multi-layer printed circuit board (PCB),but in other embodiments substrate 208 can be another type of substratesuch as wafers of silicon, single crystal silicon, silicon-on-insulator(see FIG. 4C), glass, ceramic, or low temperature co-fired ceramic(LTCC) technology.

In subassembly 202, conductive path 220 extends from contact pad 216 toprobe 214 to provide electrical power to the probe. Similarly,conductive paths 222 extend through substrate 208 to provide electricalconnection for injector electrodes 210 and 212, and conductive path 228extends through substrate 208 to provide electrical connection betweenelectrode set 224 and resistor set 226, as well as to provide a paththrough which electrical power can be supplied to electrode set 224 andresistor set 226. Finally, conductive path 229 can be used to provide anelectrical connection between detector electrode 236 and circuitry andlogic that can be used to detect the signal generated by ions arrivingat the detector electrode. In the illustrated embodiment, the conductivepaths can be a combination of metal traces and vias within thesubstrate, such as those which can be found in a multi-layer printedcircuit board or those which can be patterned, deposited and etched intoa substrate using photolithographic techniques. In other embodiments,the conductive paths can instead be printed or patterned and etched onthe surfaces of the substrate instead of going through the interior ofthe substrate. In still other embodiments, the conductive paths can beseparate components such as wires.

FIGS. 3C-3D together illustrate an embodiment of the construction ofsecond subassembly 204. Subassembly 204 includes a substrate 231 havingseveral components formed thereon. Planar electrode 234, injectorelectrodes 232 and 233, electrode set 242 and detector electrode 248 areformed on one side of substrate 231, while resistor set 226 and contactpad 236 are formed on the other side of substrate 208. The principaldifference between subassembly 204 and subassembly 202 is the presencein subassembly 204 of planar electrode 234 instead of probe 214.Subassembly 204 can be manufactured using any technique that can be usedto manufacture subassembly 202, and the variations applicable tosubassembly 202 and its components are equally applicable to subassembly204 and its components.

FIGS. 4A-4B together illustrate an alternative embodiment of aMEMS-scale micro-ISS 400. Like ISS 200, micro-ISS 400 is intended to beoperated in ambient pressure but can also be used in a vacuumenvironment. Micro-ISS 400 is fabricated on a silicon wafer 401sandwiched by a first glass wafer 402 and a second glass wafer 403. Mostof the elements of detector 400 are formed in silicon wafer 401 usingprocesses such as lithographic patterning and etching. Injectorelectrodes 404, 406, 408 and 410 are formed in silicon wafer 401. Themicro-corona ionizer is also formed in silicon wafer 401 between thepair of injector electrodes 404 and 406 and the other pair of injectorelectrodes 408 and 410. In the illustrated embodiment, the micro-coronaionizer includes planar electrodes 412 and 414. Sharp-tipped (i.e.,sharp knife-edged) probe 416 projects from planar electrode 414 towardplanar electrode 412. As in detector 200, the distance between the sharpknife-edge of probe 416 and planar electrode 412 will depend on suchfactors as the chemicals to be ionized, the voltage to be applied, andso on. The probe and discharge gap is formed directly bylithographically etching the silicon with optical mask. The gap can beprecisely defined by the optical mask design in such case. All theseparation electrodes can also be simultaneously constructed in the sameprocess.

Electrode sets 418 and 419 are also formed in silicon wafer 401, as aredetector electrodes 422 and 424. Resistors 420 can be formed on glasswafer 403 before bonding to the silicon and electrically coupled to theindividual separation electrodes within electrode set 418, whileresistors 421 can also be formed on glass wafer 403 and electricallycoupled to individual separation electrodes 419. A heater including oneor more heating elements 426 can be formed on glass wafer 403, on theside of the wafer opposite where the wafer is joined to silicon wafer401. Although not shown in the figure, conductive paths can be providedin or on silicon wafer 401, glass wafer 402 and/or glass wafer 403 toprovide the necessary electrical connections for the differentcomponents. Although micro-ISS 400 is of a different construction thanISS 200, all its elements are subject to the same variations in size,positioning, number, construction, and so on described above for theelements of ISS 200.

FIG. 4C illustrates an alternative embodiment of a micro-ISS 450.Micro-ISS 450 is in most respects similar to micro-ISS 400. The primarydifference is that in micro-ISS 450 most of the components are formed ina silicon layer 451 that forms part of a thick silicon-on-insulator(SOI) wafer that includes a base layer 452, an insulator layer 454, andsilicon layer 451. In other words, micro-ISS 450 replaces the glasswafer 403 and silicon wafer 401 of micro-ISS 400 with an SOI wafer.Glass wafer 402 is used in the same position and for the same functionas it is in micro-ISS 400. The same manufacturing techniques used formicro-ISS 400 can be used for micro-ISS 450.

FIG. 5A illustrates an alternative embodiment of a micro-ISS 500. LikeISS 400, micro-ISS 500 is intended to be operated in ambient pressurebut can also be used in a vacuum environment. In the illustratedembodiment, micro-ISS 500 is a MEMS ISS that can be manufactured in asilicon wafer sandwiched between two substrates such as glass plates, asshown in FIGS. 4A and 4B, or can be manufactured in a SOI wafer as shownin FIG. 4C. In other embodiments, ISS 500 can be manufactureddifferently and need not be a MEMS or MEMS-scale device. Additionally,all elements of micro-ISS 500 are subject to the same variations insize, positioning, number, construction, and so on described above forthe elements of detector 200.

Micro ISS 500 includes injector electrodes 504, 506, 508 and 510. Alsoformed between the injector electrodes is the micro-corona ionizer. Inthe illustrated embodiment, the micro-corona ionizer includes planarelectrodes 512 and 514. Sharp-tipped probe 516 projects from planarelectrode 514 toward planar electrode 412. As in the other describedembodiments, the discharge distance between the tip of probe 516 andplanar electrode 512 will depend on such factors as the chemicals to beionized, the voltage to be applied, and so on.

Separation electrode sets 518 and 524 are also formed in silicon wafer401, and resistors 520 can be electrically coupled to the individualseparation electrodes within separation electrode set 518, whileresistors 526 can be electrically coupled to individual separationelectrodes in separation electrode set 524. In micro-ISS 500, separationelectrode sets 518 and 524 are not spaced apart by a uniform distance Das in ISS 400, but instead the spacing between the separation electrodesets varies in the longitudinal dimension. In the illustratedembodiment, the spacing increases (i.e., it diverges) linearly withlongitudinal distance from the injector, such that the spacing at afirst longitudinal position is D1, while the spacing at a secondlongitudinal position further from the injector is D2, with D2 beinggreater than D1. In other embodiments, the spacing between separationelectrode sets need not vary linearly with longitudinal position, and instill other embodiments the spacing need not increase with longitudinalpositions but can instead decrease (converge) with longitudinalposition. In still other embodiments, the variation of spacing withlongitudinal position need not be monotonic as shown.

In micro-ISS 500, separation electrode set 518 is coupled to a directcurrent high voltage (DC-HV2) source 522, while separation electrode set524 is coupled to another direct current high voltage (DC-HV3) source528. Two or more different DC high voltages (DC-HV2 and DC-HV3) can beapplied to the separation electrodes to create both longitudinal andtransverse electric fields along the ion travel direction. In such case,different ions will travel with different curvatures and velocitiestowards the sensor electrodes 530. An array of sense electrodes 530 arepositioned at multiple designed to detect different-curvature ionsseparately, as shown in FIG. 5B.

In micro-ISS 500, an array of detector electrodes 530 is formed at theend of the drift and separation channel opposite the ion injector. Inthe illustrated embodiment, six detectors 530 are symmetricallypositioned about a centerline and are positioned at several differentlongitudinal positions. In other embodiments the number of detectors canvary, the detectors need not be symmetrically positioned about thecenterline, and the detectors need not be positioned at differentlongitudinal positions. In an embodiment where longitudinal andtransverse electric fields are created by applying different voltages tothe sets of separation electrodes, the detector array provides anadditional gas ion spatial distribution, resulting in a powerfultwo-dimensional gas/chemical spectrum pattern mapping that separatesions in both time and space, as shown in FIG. 5B. Therefore, it candrastically improve the selectivity of micro-ISS 500.

A heater including one or more heating elements (not shown) can beformed micro-ISS 500, on the side of the wafer opposite where the waferis joined to silicon wafer 401. As with ISSs 400 and 450, conductivepaths (also not shown) can be provided in or on the wafers that formmicro-ISS 500 to provide the necessary electrical connections for thedifferent components.

FIG. 6 illustrates an alternative embodiment of a micro-corona-ISS 600with separation electrodes and a sensor electrode array for 2D spectrumpattern mapping. Like the other ISS embodiments described herein,micro-ISS 600 is intended to be operated in ambient pressure but canalso be used in a vacuum environment. Micro-ISS 600 is in most respectssimilar to micro-ISS 500. The primary difference is that simple curvedseparation electrodes 618 and 620 can be designed on each side of thedrift and separation channel. A DC high voltage (HV2) is directlyapplied between the two electrodes, producing a transverse electricfield across the injected ions from the micro-corona ionizer and theinjector. Similar to configuration in FIG. 5A, gas ions with differenttraveling curvatures are detected by separate electrodes, and thus, 2Dspectrum pattern mapping can be obtained as shown, for example, in FIG.5B.

FIG. 7 illustrates an embodiment of a gas detection system 700 in whichembodiments of an ISS, such as those described above, can be used.System 700 includes a pre-concentrator 702 coupled by a fluid connectionto a gas chromatograph 704. Gas chromatograph 704 is in turn coupled bya fluid connection to ion separation spectrometer (ISS) 706, which can,in some embodiments, be any of the ISS embodiments described above. ISS706 is coupled to ion sensing, conditioning and processing circuitry andlogic 708. A control circuit and associated logic 710 is coupled tocircuitry and logic 708, as well as to pre-concentrator 702, gaschromatograph 704 and ISS 706.

Pre-concentrator 702 includes an inlet through which a gas sample entersan outlet coupled to gas chromatograph 704. As the gas sample flowsthrough pre-concentrator 702, the pre-concentrator absorbs certainchemicals from the gas sample, thus concentrating those chemicals forlater separation and detection. In one embodiment of system 700pre-concentrator 702 can be a MEMS pre-concentrator, but in otherembodiments pre-concentrator 702 can be a non-MEMS chip scale device.

Gas chromatograph 704 includes an inlet coupled to pre-concentrator 702and an outlet coupled to ISS 706. Gas chromatograph 704 receives fluidfrom pre-concentrator 702 and outputs fluid to ISS 706. As fluidreceived from pre-concentrator 702 flows through gas chromatograph 704,individual chemicals in the gas sample received from thepre-concentrator are separated from each other in the time domain forlater input into ISS 706. In one embodiment of system 700 gaschromatograph 704 can be a MEMS gas chromatograph, but in otherembodiments gas chromatograph 108 can be a non-MEMS chip scale device.

ISS 706 is coupled to gas chromatograph 704. As fluid flows into ISS706, the chemicals that were not separated by gas chromatograph 704enter the ISS and their presence and/or concentration is sensed bysensors within the ISS, as described above. ISS 706 achieves ionizedgases/chemical separation and sensing, for chemicals which are notseparated by the micro-GC chip. As a result, it provides the 2nd stagegases/VOCs separation, which further improves the system's selectivitybetween similar gas or chemical analytes. When ISS 706 is configured andintegrated with pre-concentrator 702 and gas chromatograph 704 in thesame system as shown in FIG. 7, it can reach gas/chemical limit ofdetection (LOD) in range of parts-per-billion (ppb) to part-per-trillion(ppt).

Sensing, conditioning and processing circuit 708 is coupled to an outputof ISS 706 such that it can receive data signals from individual sensorswithin ISS 706 and process and analyze these data signals. In oneembodiment, circuit 708 can be an application-specific integratedcircuit (ASIC) designed specifically for the task, such as a CMOScontroller including processing, volatile and/or non-volatile storage,memory and communication circuits, as well as associated logic tocontrol the various circuits and communicate externally. In otherembodiments, however, circuit 708 can instead be a general-purposemicroprocessor in which the control functions are implemented insoftware. Although shown in the figure as having all threefunctions—sensing, conditioning and processing—in other embodimentsthese functions need not all be present, or can be present in differentcircuits. Circuit 708 is also coupled to control circuit 710 and cansend signals to, and receive signals from, control circuit 710 so thatthe two circuits can coordinate and optimize operation of system 700.Although the illustrated embodiment shows control circuit 710 andcircuit 708 as physically separate units, in other embodiments thecontroller and the readout and analysis circuit could be combined in asingle unit.

Control circuit 710 is communicatively coupled to the individualelements within system 700 such that it can send control signals and/orreceive feedback signals from the individual elements. In oneembodiment, control circuit 710 can be an application-specificintegrated circuit (ASIC) designed specifically for the task, forexample a CMOS controller including processing, volatile and/ornon-volatile storage, memory and communication circuits, as well asassociated logic to control the various circuits and communicateexternally to the elements of system 700. In other embodiments, however,control circuit 710 can instead be a general-purpose microprocessor inwhich the control functions are implemented in software.

The above description of illustrated embodiments of the invention,including what is described in the abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize. These modifications can bemade to the invention in light of the above detailed description.

The terms used in the following claims should not be construed to limitthe invention to the specific embodiments disclosed in the specificationand the claims. Rather, the scope of the invention is to be determinedentirely by the following claims, which are to be construed inaccordance with established doctrines of claim interpretation.

1. An apparatus comprising: an ion injector having an inlet and anoutlet; a micro-corona ionizer positioned between the inlet and theoutlet of the ion injector, the micro-corona ionizer including: a planarelectrode; and a sharp knife-edged electrode spaced apart from theplanar electrode and positioned with the sharp knife edge pointingtoward the planar electrode; a drift and separation channel having afirst end and a second end, the first end being coupled to outlet of theion injector; and an ion detector coupled to the second end of the ionseparation and drift channel.
 2. The apparatus of claim 1, furthercomprising a voltage source coupled to the planar electrode and thesharp knife-edged electrode.
 3. The apparatus of claim 1 wherein the ioninjector comprises: a first pair of injection electrodes; and a secondpair of injection electrodes spaced apart from the first pair ofinjection electrodes.
 4. The apparatus of claim 3 wherein themicro-corona ionizer is positioned between the first pair of injectionelectrodes and the second pair of injection electrodes.
 5. The apparatusof claim 3, further comprising a voltage source coupled between thefirst pair of injection electrodes and the second pair of injectionelectrodes.
 6. The apparatus of claim 1 wherein the drift and separationchannel comprises: a first channel wall having a first set of separationelectrodes thereon; and a second channel wall having a second set ofseparation electrodes thereon, wherein the second set of separationelectrodes is spaced apart from the first set of separation electrodes.7. The apparatus of claim 6, further comprising: a voltage sourcecoupled to the first set of separation electrodes; and a voltage sourcecoupled to the second pair of separation electrodes.
 8. The apparatus ofclaim 7 wherein the voltage applied to the first set of separationelectrodes is different than the voltage applied to the second set ofseparation electrodes.
 9. The apparatus of claim 6 wherein the spacingbetween the first set of separation electrodes and the second set ofseparation electrodes is constant.
 10. The apparatus of claim 6 whereinthe spacing between the first set of separation electrodes and thesecond set of separation electrodes varies from the first end of thechannel to the second end of the channel.
 11. The apparatus of claim 1wherein the ion detector comprises an array of at least two sensorelectrodes positioned about a centerline of the drift and separationchannel.
 12. The apparatus of claim 11, further comprising a readingcircuit and logic coupled to the array of sensor electrodes to sense andread signals generated by each sensor electrode.
 13. The apparatus ofclaim 12, further comprising a conditioning circuit and logic coupled tothe reading circuitry to condition signals received from the readingcircuit.
 14. A process comprising: ionizing chemicals in a gas sampleusing a micro-corona ionizer, wherein ionizing chemicals comprises:directing the gas sample into a space between a planar electrode and asharp knife-edged electrode spaced apart from the planar electrode,wherein the sharp knife-edged electrode is positioned with the sharpknife edge pointing toward the planar electrode, and applying a voltagebetween the planar electrode and the sharp knife-edged electrode;injecting the ionized chemicals into a drift and separation channel;time-domain separating the chemical ions from each other in the driftand separation channel; and detecting the separated chemical ions. 15.The process of claim 14 wherein injecting the ionized chemicalscomprises: positioning the ionized chemicals between a first pair ofinjection electrodes and a second pair of injection electrodes spacedapart from the first pair of injection electrodes; and applying avoltage between the first pair of injection electrodes and the secondpair of injection electrodes.
 16. The process of claim 14 whereintime-domain separating the chemical ions from each other comprises:injecting the chemical ions into a drift and separation channel betweena first set of separation electrodes and a second set of separationelectrodes spaced apart from the first set of separation electrodes; andapplying a voltage to the first set of separation electrodes and to thesecond set of separation electrodes.
 17. The apparatus of claim 16wherein the voltage applied to the first set of separation electrodes isdifferent than the voltage applied to the second set of separationelectrodes.
 18. The process of claim 14 wherein detecting the separatedchemical ions comprises: receiving the time-domain separated chemicalions at an array of at least two sensor electrodes; and generating asignal in each electrode indicative of the ions received at thatelectrode.
 19. The process of claim 18, further comprising reading thesignals generated by the sensor electrodes.
 20. The process of claim 19,further comprising conditioning signals read from the sensor electrodes.21. A system comprising: a gas chromatograph having an inlet and anoutlet; a detector coupled to the outlet of the gas chromatograph, thedetector comprising: an ion injector having an inlet and an outlet,wherein the inlet of the ion injector is coupled to the outlet of thegas chromatograph; a micro-corona ionizer positioned between the inletand the outlet of the ion injector, the micro-corona ionizer comprising:a planar electrode, and a sharp knife-edged electrode spaced apart fromthe planar electrode and positioned with the sharp knife edge pointingtoward the planar electrode; an ion separation and drift channel havinga first end and a second end, the first end being coupled to outlet ofthe ion injector; and an ion detector coupled to the second end of theion separation and drift channel.
 22. The system of claim 21, furthercomprising a voltage source coupled to the planar electrode and thesharp knife-edged electrode.
 23. The system of claim 21 wherein the ioninjector comprises: a first pair of injection electrodes; and a secondpair of injection electrodes spaced apart from the first pair ofinjection electrodes.
 24. The system of claim 23 wherein themicro-corona ionizer is positioned between the first pair of injectionelectrodes and the second pair of injection electrodes.
 25. The systemof claim 23, further comprising a voltage source coupled between thefirst pair of injection electrodes and the second pair of injectionelectrodes.
 26. The system of claim 21 wherein the drift and separationchannel comprises: a first channel wall having a first set of separationelectrodes thereon; and a second channel wall having a second set ofseparation electrodes thereon, wherein the second set of separationelectrodes is spaced apart from the first set of separation electrodes.27. The system of claim 26, further comprising: a voltage source coupledto the first set of separation electrodes; and a voltage source coupledto the second pair of separation electrodes.
 28. The system of claim 27wherein the voltage applied to the first set of separation electrodes isdifferent than the voltage applied to the second set of separationelectrodes.
 29. The system of claim 26 wherein the spacing between thefirst set of separation electrodes and the second set of separationelectrodes is constant.
 30. The system of claim 26 wherein the spacingbetween the first set of separation electrodes and the second set ofseparation electrodes varies from the first end of the channel to thesecond end of the channel.
 31. The system of claim 21 wherein the iondetector comprises an array of at least two sensor electrodes positionedabout a centerline of the drift and separation channel.
 32. The systemof claim 31, further comprising a reading circuit and logic coupled tothe array of sensor electrodes to sense and read signals generated byeach sensor electrode.
 33. The system of claim 31, further comprising aconditioning circuit and logic coupled to the reading circuit tocondition signals received from the reading circuit.
 34. The system ofclaim 33, further comprising a processing circuit and logic coupled tothe conditioning circuitry to process the conditioned signals.
 35. Thesystem of claim 34, further comprising a control circuit and logiccoupled to the ion sensor, the gas chromatograph, and the processingcircuit.
 36. The system of claim 21, further comprising apre-concentrator coupled to the inlet of the gas chromatograph.